Electrical ground filter means for boats supplied with a shore-based source of alternating current power

ABSTRACT

An electrical ground filter means for boats or other vessels supplied with a shore-based source of alternating current power having current leads and an electrical grounding lead connected between the alternating current source and a boat, the ground filter means comprising a first pair of rectifiers in series with each other, a second pair of rectifiers in series with each other and of opposite polarity with the first pair, a capacitor means, the first and second pairs of rectifiers and the capacitor means being connected electrically in parallel of each other.

United States Patent Stephens, Jr. et al. [4 1 Jan. 18, 1972 ELECTRICALGROUND FILTER References Cited MEANS FOR BOATS SUPPLIED WITH A UNITEDSTA'l ES PATENTS SHORE-BASED SOURCE OF 1 055 327 3/1913 H 307/95 URRE NEenng ALTERNATING C NT Po R 3,383,520 5/1968 Hoffman ..307/95 [72]Inventors: Frank H, Stephens, Jr,, Morristown; Paul 3,477,931 11/1969Veda et a1 ..204/196 X B. Byrne, Warren; Edward P. Anderson, Livingston,all of NJ, Primary Examiner-James D. Trammell l At l h J 73 Assignee:Engelhard Minerals & Chemicals Corporasame n and G 57 ABSTRACT [22]Filed: 1970 An electrical ground filter means for boats or other vessels[21] APPL 90,2 supplied with a shore-based source of alternating currentpower having current leads'and an electrical grounding lead connectedbetween the alternating current source and a boat, [52] US. Cl. ..317/l8D, 204/147, 204/ 196, the ground filter means comprising a first pair ofrectifiers in 307/95 317/20 series with each other, a second pair ofrectifiers in series with [51] Int. Cl. ..H01b 7/28 each other and ofopposite polarity with the first pair a [58] Field of Search ..307/95;204/196, 147, DIG. 5, capacitor means, the fi and second pairs frectifiers and 204/D1G. 6; 136/163, 182; 317/10, 18 D, 20

co U II LOCATION OF GROUND FILTER the capacitor means being connectedelectrically in parallel of each other.

. 5. Q2995 v a vr lisu POWER SYSTEM GROUND PATENTEB JAN 1 e 1972 sum 1or 2 ELECTRICAL LOCATION OF GROUND FILTER POWER SYSTEM GROUND I- AMPERES.OOOO| V- VOLTS INVENTORS: FRANK H. STEPHENS J, PAUL B. BYRNE EDWARD P.ANDERSON 2.2. A

AGENT ELECTRICAL GROUND FILTER MEANS FOR BOATS SUPPLIED WITH ASHORE-BASED SOURCE OF ALTERNATING CURRENT POWER BACKGROUND OF THEINVENTION It is most practical for boats or other vessels to obtainelectrical power from a shore-based source while the boat or vessel isat dock rather than from on-board electrical generation equipment. Thewiring of this electricity aboard the vessel is often responsible forexcessive corrosion of the water-immersed metal structure of the vessel.

Two corrosion promoting situations may exist in a boat wired forshore-based power. One situation is that when a third wire groundingconductor is used to ground a metal hull or metal underwater structures,a galvanic condition exists between the boat and shore-located metalstructures. If the boat hull is an aluminum hull, or a fiber glass hullequipped with aluminum outdrives or outboard motors, the aluminum tendsto become a sacrificial anode which will corrode away to protectshore-located iron structures. The other situation is that should a boathave a steel hull the galvanic action may not be as highly destructiveas with aluminum, but the protection intended from cathodic protectiondevices with which the boat may be equipped can be seriously attenuatedby a parasitic drain through the third wire ground.

Deterioration from these situations is costly since it causes structuralweakness and surface roughness of the boat hull or its underwater metalstructures. Corrosion so induced is most active in limited areas of thenull and may promote water leakage. Also, a roughened surface increasesresistance to the movement of the boat through water and therebyadversely affects the efficiency-of boat operation.

It is the purpose of this invention to provide a means for eliminatingthe potential corrosion damage to boats or other vessels havingelectrically grounded metal hull structures, while at the same time toprovide protection to personnel aboard the boat or vessel fromelectrical shock.

SUMMARY OF THE INVENTION In accordance with the invention there isprovided an electrical ground filter means for boats or other vesselssupplied with a shore-based source of alternating current power, such asan appropriate transformer, having current leads and an electricalgrounding lead connected between the source of current and a boat orvessels, the ground filter means being connected in series with thegrounding lead, the filter means comprising a first pair of rectifiersin series with each other, a second pair of rectifiers in series witheach other and of opposite polarity with the first pair, a capacitor ora .pair of capacitors, the pair of capacitors being in series with eachother and having opposite polarities, the first and second pairs ofrectifiers and the capacitor or the pair of capacitors being connectedelectrically in parallel of each other. The parallel combination of thecapacitor or the pair of capacitors and rectifiers provides lowimpedance under usual operating current conditions while simultaneouslypreventing the passage of direct current at low voltages inherent in thecorrosion process.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a schematic view of anelectrical system for a boat supplied with a shore-based source ofalternating current power including the filter means of the invention.

FIG. 2 illustrates a schematic circuit representation of the filtermeans of the invention,

FIG. 3 is a graphic representation of the volt-ampere characteristics ofeach series connected pair of the rectifier components of the groundfilter means,

FIG. 4 is a graphic representation of the volt-ampere characteristics ofthe combined pairs of rectifiers in parallel arrangement includingalternating current capacitor impedance, and

FIG. 5 is a graphic representation of a composite curve showing thevolt-ampere characteristics and alternating current capacitor impedanceof the parallel combination of rectifier pairs and capacitor means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, boat 1 issupplied with a shore-based source of alternating current powercomprising a transformer 2 having a primary winding 3 and a secondarywinding 4. The power system transfonner output from the secondarywinding is grounded by means of grounding lead 5 at the shore location.Current leads 6 and 7 and grounding lead 8 pass from the transformersecondary winding to a location on boat 1,

preferably through a disconnectable means comprising a female socket 9and male plug 10. The current leads 6 and 7 are connectable to a poweroutlet (not shown) on board the boat while the grounding lead 8 isgrounded to the boat hull, as at 9, through an electrical ground filtermeans 11 preferably located on the boat. The ground filter means isconnected is series in the grounding lead 8 as more particularly shownin FIG. 2. The filter means comprises a first pair of rectifiers l2 and13 in series with each other, a second pair of rectifiers 14 and 15 inseries with each other and of opposite polarity with the first pair ofrectifiers, a capacitor means, for example a pair of capacitors l6 and17 in series with each other and of opposite polarities, the first andsecond pairs of rectifiers and the capacitor means, e.g., capacitors l6and 17, being connected in lead 8 in parallel with each other as shown.

The rectifiers are merely schematically shown since in practice the fourrectifiers may be manufactured as a single-piece semiconductor device.

In order to prevent galvanic corrosion it is necessary to restrict thepassage of low-voltage direct current between the boat and the shore. Itis known that the maximum potential difference that will be generatedbetween any two dissimilar metals (excepting when one metal ismagnesium) immersed in a common sea water electrolyte is 1.1 volt. FIG.3 shows that at this voltage a current of the order of amperes will flowthrough a single rectifier (point A). When two such rectifiers areplaced electrically in series and 1.1 volt is impressed across thiscombination, for example rectifiers l2 and 13, the voltage across eachrectifier will be approximately 0.55 volt. FIG. 3 shows. that at thisvoltage the current flowing will be less than 0.001 ampere (point B).When reverse polarity is applied to this rectifier combinationessentially zero current flows. Since the voltage between the vessel andshore installations may be of either polarity depending on the metalsencountered, it is necessary to employ rectifiers arranged with bothpolarities. This is shown in FIG. 2 where rectifiers I2 and 13 of onepair of rectifiers are connected in series with each other, rectifiersl4 and 15 of another pair of rectifiers are connected in series witheach other and these pairs are connected electrically in parallel. Thepairs of rectifiers are of opposite polarities relative to each other.The direct current volt-ampere characteristics of this arrangement isshown in FIG. 4 by the dashed curves. At low currents the combination ofrectifiers has high impedance, e.g., at Ll volt at 0.001 ampere or anapparent resistance of 1,100 ohms, while at high currents a lowimpedance is observed, e.g., 1.8 volt at 40 amperes or an apparentresistance of 0.045 ohm. The combination of both these pairs ofrectifiers performs the required function of a low impedance faultcurrent path while simultaneously preventing the passage of directcurrent at the low voltages inherent in the corrosion processes. Tofurther improve the performance of the filter a capacitor meansconstructed, for example, of a single nonpolar capacitor, or a pair ofpolarized electrolytic capacitors 16 and 17 which are connected inseries with opposing polarities are employed. This capacitor means soarranged with the rectifiers reduces the alternating current terminalimpedance of the filter means at potentials below that at which therectifiers conduct. This type of capacitor means can be made to have alarge capacitance at low voltages, for example 014 farad at 3 volts. Ata power line frequency of 60 hertz this capacitor means has an impedanceof 0.04 ohm and is shown by the solid line in FIG. 4. This impedance isless than the apparent impedance of the rectifier system of rectifiers12, 13, 14 and 15 at currents less than 30 amperes alternating current.

The parallel combination of capacitors and rectifiers provides lowimpedance under all current conditions at low power dissipation. Thecomposite volt-ampere characteristics of the filter at a frequency of 60hertz is illustrated by FIG. 5.

The grounding lead 8 is installed to prevent serious electrical shock tothe user of faulty electrical devices with shorts or leakage to theirenclosure. It is necessary to preserve the electrical integrity of thisgrounding lead in the event of high short circuit currents which mayexceed 1,000 amperes. The rectifiers employed are designed to meet thishigh fault current requirement.

The rectifiers l2, 13, 14 and 15 described each consist of a P- andN-doped silicon semiconductor junction. It is possible to fabricatethese four junctions on a single piece of semiconductor material andprovide the volt-ampere characteristics shown by the dashed line in FIG.4.

In a more generic sense, the invention comprises an electrical groundfilter for the elimination of corrosive galvanic currents which isseries connected between two dissimilar metals disposed in a commonelectrolyte, the filter having an impedance less than 0.] ohm toalternating currents of 60 hertz and an impedance of at least 1,000 ohmsat voltages of up to 0.9 volt direct current and the ability to passfault currents in of at least 1,000 amperes.

Various modifications of the filter means of the invention iscontemplated within the scope of the appended claims.

1. An electrical ground filter means for vessels supplied with ashore-based source of alternating current power, current leads and anelectrical grounding lead connected between the power source and thevessel, the ground filter means being connected in series with thegrounding lead, the filter means comprising a first pair of rectifiersin series with each other, a second pair of rectifiers in series witheach other and of opposite polarity with the first pair of rectifiers, acapacitor means, the first and second pairs of rectifiers and thecapacitor means being connected electrically in parallel with eachother.

2. An electrical ground filter means according to claim 1, wherein thecapacitor means comprises a pair of capacitors in series with each otherand of opposite polarities.

3. An electrical ground filter means according to claim 1, wherein thefirst and second pairs of rectifiers are in the form of a single-piecesemiconductor device.

4. An electrical ground filter means for the elimination of corrosivegalvanic currents, the filter means being electrically series connectedbetween two dissimilar metals disposed in a common electrolyte, thefilter means having an impedance less than 0.1 ohm to alternatingcurrents of 60 hertz and an impedance of at least 1,000 ohms at voltagesof up to 0.9 volt direct current 5. An electrical ground filter meansaccording to claim 4, wherein the filter means is characterized by thepassage of fault currents of at least 1,000 amperes.

1. An electrical ground filter means for vessels supplied with ashore-based source of alternating current power, current leads and anelectrical grounding lead connected between the power source and thevessel, the ground filter means being connected in series with thegrounding lead, the filter means comprising a first pair of rectifiersin series with each other, a second pair of rectifiers in series witheach other and of opposite polarity with the first pair of rectifiers, acapacitor means, the first and second pairs of rectifiers and thecapacitor means being connected electrically in parallel with eachother.
 2. An electrical ground filter means according to claim 1,wherein the capacitor means comprises a pair of capacitors in serieswith each other and of opposite Polarities.
 3. An electrical groundfilter means according to claim 1, wherein the first and second pairs ofrectifiers are in the form of a single-piece semiconductor device.
 4. Anelectrical ground filter means for the elimination of corrosive galvaniccurrents, the filter means being electrically series connected betweentwo dissimilar metals disposed in a common electrolyte, the filter meanshaving an impedance less than 0.1 ohm to alternating currents of 60hertz and an impedance of at least 1,000 ohms at voltages of up to 0.9volt direct current
 5. An electrical ground filter means according toclaim 4, wherein the filter means is characterized by the passage offault currents of at least 1,000 amperes.